High pressure steam purifier



March 27, 1956 w. B. GURNEY HIGH PRESSURE STEAM PURIFIER 2 Sheets-Sheet1 Filed Aug. 12, v1952 INVENTOR M7 [1am Brewster 6 1227295 ATTO R N EYMarch 27, 1956 w GURNEY 2,739,663

HIGH PRESSURE STEAM PURIFIER Filed Aug. 12, 1952 2 Sheets-Sheet 2INVENTOR. Mil/jam Bren safer 621m 9;

ATTORNEY United States Patent EHGH PRESSURE STEAM PURIFIER WilliamBrewster Gurney, Baton Rouge, La. Application August 12, 1952, SerialNo. 303,948

8 Claims. (Cl. 183-1) The present invention relates to a method of andapparatus for the purification of steam, and more particularly to themethod and apparatus for the removal of contaminants from saturatedsteam by adiabatic expansion of the steam. This application is acontinuation in part of my application, Serial No. 235,872, filed July9, 1951, and now abandoned.

High pressure steam generated for power process usually contains minoramounts of impurities such as silica and other water salts, which duringthe transformation of energy in an associated turbine frequently isdeposited on the blade surfaces and other internal parts of the turbine.An accumulation of such deposits results in reduced turbine efiiciencyand loss of its availability while the deposits are being removed.

The transportation of contaminating matter by the steam is generallyconsidered to occur either by mechanical entrainment, by vapor orsolution in the steam, or by a combination of these processes.Mechanical entrain ment can be reduced by efiicient separation of liquidand vapor through the use of centrifugal forces, providing the physicalproperties of the liquid-vapor mixture are conducive to mechanicalseparation.

According to the Mollier diagram for steam, saturated steam at apressure above 450 pounds per square inch absolute (p. s. i. a.) passesthrough a moisture zone as the steam pressure is reduced without loss ofheat. Further reduction in the steam pressure causes the steam to passthrough the saturated steam line into the superheated steam zone.

1 have discovered that a major portion of the impurities in the steamdischarged from a steam generator can be eliminated by the condensationof a small part of the steam generated. Apparently, the condensedmoisture forms minute droplets about a nuclae of solid impurity presentwith the steam. In any event, the condensed moisture droplets areseparated from the steam and withdrawn from the steam and waterseparators out of contact with the steam strain. The collected watercontains a major portion of the impurities present in the saturatedsteam generated in the unit, including a high percentage of silica.

The condensation of moisture in steam can be accomplished by a reductionin pressure of the steam. The steam pressure reduction may be adiabaticand effective when the dry saturated steam pressure is in excess of 450p. s. i. a. The expansion of the steam can be accomplished by flowthrough an orifice, nozzles, or the like.

The various features of novelty which characterize my invention arepointed out with particularity in the claims annexed to and forming apart of this specification. For a better understanding of the invention,its operating advantages and specific objects attained by its use,reference should be had to the accompanying drawings and descriptivematter in which I have illustrated and described an embodiment of theinvention.

Of the drawings:

Fig. 1 is a transverse view, in section, of a steam and water drumincorporating an embodiment of the invention;

Fig. 2 is a partial transverse section of a steam and water drum showinga modified form of the invention;

Fig. 3 is a somewhat diagrammatic view of a steam and water drum and asuperheater inlet header incorporating structure according to theinvention,

Fig. 4 is an enlarged view of a portion of the apparatus shown in Fig.3;

Fig. 5 is a diagrammatic view of a steam purity testing apparatuscontaining structure according to the principle of the presentinvention; and

Fig. 6 is a plan view of a portion of the apparatus shown in Fig. 5.

Referring to Fig. 1, the invention is exemplified as installed in thesteam and water drum 10 of a steam generating unit. A mixture of steamand water is delivered through tubes 11 to the drum 10, water passesfrom the drum through downcomer tubes 12 into the circulating system ofthe steam generating unit, while saturated steam is discharged throughrows of tubes 13 positioned in the upper portion of the drum 10. Thesteam and water mixture entering the tubes 11 discharges into a chamber14 which is formed by a series of connected plates 15 mounted internallyof the boiler drum. A series of horizontally spaced vertical elongatedducts 16 connect chamber 14 with a row of cyclonic steam separators 17.The general construction of the cyclonic type separator and theconnecting chamber 14 is disclosed in detail in U. S. Patent 2,368,211.

As described in the patent and shown in Fig. 1, each separator isprovided with a bottom outlet 18 at the lower end and an upper outlet 20at the upper end thereof. Steam and water are separated within theseparators 17 by centrifugal forces with the steam passing upwardlythrough the outlet 20 and the separated water discharging downwardlythrough the outlet 18. Ordinarily the water level within the drum 10 ismaintained approximately at the horizontal center line of the drum. Thewater level may vary above or below the drum center line in the courseof operations, but should not vary beyond the general limits of theheights of the cyclonic separator 17 The steam leaving the outlet 2! ofthe cyclonic separators is substantially dry and in a saturatedcondition, although it is possible for the steam to be slightlysuperheated, saturated, or to contain a small amount of moisture. Themoisture would be in the form of minute droplets which are extremelydifficult to separate from the steam by ordinary mechanical means.

The steam passing through the cyclone separators 17 and toward the tubes13 is directed through a secondary steam and Water separator 21. Thesecondary separator is formed from a series of corrugated platesarranged in parallel and lying in a series of planes generallyperpendicular to the longitudinal axis of the drum 10. This constructionis well known. On the steam entry side of the separator 21 is positioneda plate 24 which is provided with a plurality of orifices 25. Inwardlyof the separators 21 is a dry steam collecting chamber 22 openingdirectly to the tubes 13. The lower portions of the separators 21 areprovided With a moisture collecting cham ber 23 and plates 26. In theconstruction described, the steam passing through the orifices 25expands with the condensation of moisture therein which is collected bycontact with the corrugated plates of the secondary separators. Themoisture collecting upon the separator plates flows downwardly into thechamber 23 and thence through discharge pipes 27 which open to the lowerportion of the drum 10 beneath the surface of water maintained therein.

The expansion of the steam with the condensation of spanner moisturetherein produces droplets having sufiicient dimensions to be trapped bythe separator plates and removed from the moving stream so that thesteam discharging through .the tubes .13 is substantially .dry and of ahigh purity.

The alternate construction shown in .Fig. .2 illustrates a somewhatdifiierent type of steam separating means. As shown, the shell 40 of thesteam and water drum is provided with steam, or .steam and watermixture, supply tubes 41 and steam outlet tubes 42. The steam enteringthrough the tubes 41 passes downwardly and around the edge of baffieplates 43 to enter a steam and water separator 48 through a plate 44having a multiplicity of perforations 39 therein. In passing through theperforations of the plate 44 the steam is expanded with the condensationof moisture therein. The moisture is separated from the steam in theseparator 48, which may be of the general type previously described inconnection with the separators 21 shown in Fig. l. The steam leaving theseparators 48 passes through a perforated plate 45 before entering thesteam outlet tubes 42. As shown, the separators are supported from upperplates 47 attached to the shell 40 and a lower structure which includesa longitudinally extending plate 46 and a series of radial drainpassageways 50 forming a bottom closure and leading to a discharge pipe51. The pipe 51 extends downwardly from the mid-point of the structureand the passageways 50, and is provided with a valved branch connection.53 terminating beneath the water level main tained in the drum, and avalved branch connection 52 which extends through the shell 40 of thedrum.

The structure shown in Fig. 2 is primarily intended to receivesubstantially dry steam through the tubes 41, as for example where thedrum defined by the shell 40 represents the steam drum of a steamgenerating unit having multiple steam and water drums. However, amixture of steam and water from steam generating tubes can be deliveredto the drum through the tubes 41 with the separator 48 removing moisturefrom the steam. Under the latter circumstances, the tubes 42 maydischarge to an external device for further steam expansion and removalof the steam impurities in the moisture condensed therefrom.

The apparatus shown in Fig. 3 schematically illustrates a steam andwater drum .60 having steam inlet pipes 61 opening to a primary steamand water separator 64. The separator 64 may be of the general cyclonictype described in Fig. 1. The substantially dry steam leaving theseparator 64 passes through a secondary separator ,65 in its flow towardthe steam outlet tubes 63. The water separated from the steam in theprimary separator is discharged downwardly beneath the level 68 of thewater maintained in drum 60. The moisture separated from the steam bythe secondary separators 65 discharges through a drainpipe 66 to eitherof the valved branch pipes 67 or 70. The branch drainpipe 67 dischargesthe moisture outside of the boiler drum, while the branch pipe 70discharges the moisture beneath the level 68 of the water. Thesubstantially dry steam leaving the drum 60 through the tubes 63tangentially enters a cylindrical vessel 71 where the moisture isseparated from the steam by centrifugal force. The collected moisture isdischarged from the bottom of the vessel 71 to the atmosphere throughthe valved pipe 74 or to a reservoir '76 through the valved pipe 75. Thesteam passes around the lower end of a centrally located cylindricalbafile 72 positioned in the upper portion of the vessel 71 to dischargethrough a tube 73 which opens into a superheater inlet header 77.

The superheater inlet header 77 is illustrated in Figs. 3 and 4. wherethe entering steam from the tube 73 passes in a generally radialdirection .as .directed by a baffle 85 toward an axially disposedmanifold 83. The manifold is provided with a series of longitudinalspaced inlet ports 87 and a series of radially disposed exhaust tubes84.

4 The tubes extend through and beyond the wall of the header 87 and areoverlapping'ly engaged by a correspending series of tubes 78 which arewelded to the header 77 and connected with the legs of a superheater(not shown).

The longitudinal baflle 85 is attached to a longitudinally extendedperforated bafiie which follows, in general, the contour of the header'77 and is attached at its opposite end 'to the avail of the header 77adjacent the tubes 84. The steam entering through the tubes 73 isexpanded with the moisture formed by the expansion of the steam passedthrough the perforations of the plates 86, for discharge through adrainpipe 81. The pipe 81 opens to a reservoir 82 and is furtherprovided with a branch by-pass pipe 80 opening to the atmosphere. Bothof the pipes 81 and 80 are provided with valves to control the flow ofsteam through either.

As herein before described, several methods of obtaining a suitableexpansion of high pressure saturated steam .are possible. Each of thedescribed arrangements .of apparatus will attain the purity resultsadvantageously accomplished 'by the invention. It will be appreciatedthat the reduction in pressure necessary for steam purification isgreater than the ordinary pressure reduction obtained in passingsaturated steam through the customary steam and water separators. Ingeneral, the steam purification feature of the invention is applicableto saturated steam at an initial pressure in excess of 450 p. s. i. a.At each of the steam pressures above that given, a reduction in pressurewill result in the formation of a mixture of steam vapor and liquidwater because the latent heat of the vapor is higher at the reducedpressure. For example, the approximate maximum moisture content insaturated steam, assuming adiabatic expansion, can be attained at alower pressure according to the following table:

A rox. Red ed Pres- Approx-Pep V sure 5 i a cent Moisture InitialPressure, p. s. 1..a. for f i obtained by ture of cbndenpressurre reducsation non 440 Slight 450 1.0 490 2. 0 500 3-0 520 4. 0

An example of the calculations used in determining the above moisturefigures is as follows:

Moisture increase due to drop in steam pressure from 77.5 p. s. .i. a.to 650 p. s. i. a.

Heat in Liquid gg g g at saturation Latent heat .p. s. i. a. ertemperature in B. t. u. Tom 0 R in Bpbtfnpci per per pound (Assume the775 p. s. i. a. saturated steam to contain .2% moisture. Let X qual theunknown moisture content present at 650 p. s. i. a., after adiabaticexpansion of the saturated steam.)

X=4.388/720.5=0.00608 or 0.61%

0.60.80.2=0.408% increase in moisture due to the steam pressure droppingfrom 775 p. s. i. a. to 650 p. .s. 1. a.

1 have found that it is not necessary to reduce the pressure of thesaturated steam as much as indicated in the above table, .for example, areduction in pressure from 65010 "645 p. s. i. g. caused suflicientcondensation of moisture in the steam to remove a large portion of theimpurities, particularly silica, in the saturated steam.

As shown in Fig. 5 the principle of expanding steam to produce moisturetherein, and separating and collecting the moisture with the steamimpurities therein can be used for test purposes. As shown in thedrawing, a steam header 91 is provided with a sample nozzle andcollecting pipe 92 leading tangentially into a closed cylindrical vessel90. The pipe 92 is provided with throttle valves to regulate the flowand pressure drop of steam from the nozzle into the vessel 90. Thevessel is provided with a cylindrical baffie 88 positioned in the upperpart of and depending from the top of the vessel and surrounding thesteam outlet pipe 93. A water discharge pipe 95 is connected to thebottom of the vessel 90 and connects with a conventional degassing andconductive test apparatus 96. The steam pipe 93 leads to a correspondingdegassing and conductive test apparatus 97. With the apparatus describeda sample of the steam passing through the pipe 91 is discharged at areduced pressure into the vessel 90 so that the condensation recoveredfrom the condensed steam is directed to one test apparatus while thesteam remaining from the sample is directed to a companion test aparatuswhereby the conductivity of both the purified steam and the contaminatedmoisture obtained from the steam sample can be compared.

The portion of Fig. 5 relating to steam conductivity test apparatus andidentified by numerals 96 and 97 is well known and is described in theTransactions of the A. S. M. E., November 1940, vol. 62, No. 8, on page728.

It will be noted that in all phases of the invention, saturated steam ina substantially dry condition is expanded to condense moisture therein,the condensed moisture is separated from the stream and discharged outof contact with the remaining steam flow. A major portion of theimpurities in the steam will be present in the condensed moisture, andthe steam discharging from the apparatus will be in a substantially purecondition.

While in accordance with the provisions of the statutes I haveillustrated and described herein preferred embodiments of the invention,those skilled in the art will understand that changes may be made in themethod of operation and form of the apparatus disclosed withoutdeparting from the spirit of the invention covered by my claims, andthat certain features of the invention may sometimes be used toadvantage without a corresponding use of other features.

What is claimed is:

1. Apparatus for purifying steam which comprises means for separatingentrained water from saturated steam, means for adiabatically expandingthe substantially dry saturated steam for the condensation of moisturetherein, and means for separating the condensed moisture from saidexpanded steam.

2. Apparatus for purifying steam comprising a source of generally drysaturated steam, nozzle means for the expansion of said steam wherebymoisture is condensed therein, steam and Water separating means in theflow path of said expanded steam, and means for the separate dischargeof collected moisture therefrom.

3. Apparatus for purifying steam comprising a steam and water drumhaving a steam outlet in the upper portion thereof and tubes opening tosaid drum for the admission thereto of a mixture of steam and water,steam and water separators within said drum for the upward flow ofgenerally dry steam therefrom, nozzle means for the expansion of saidsteam within said drum whereby moisture is condensed from said steam,and means for collecting and discharging said condensed moisture out ofthe path of said expanded steam.

4. In a steam and water drum having a steam outlet in the upper portionand a water outlet in the lower portion thereof, means for supplying amixture of steam and water to said drum, steam and water separatingmeans within said drum arranged to receive the steam and water mixturesupplied to said drum, said separating means discharging substantiallydry steam into the upper portion of and water into the lower portion ofsaid drum, closely spaced baflle plates forming a secondary steam andwater separator in the upper portion of said drum interposed in the flowpath of steam toward said upper drum outlet, an orifice plate positionedin the path of the dry steam entering said secondary separator, andmeans for collecting separated water from said secondary separator anddischarging said collected water into the lower portion of said drum.

5. In a steam generator having a steam and water drum, means forsupplying a steam and Water mixture to said drum, means within said drumfor separating entrained water from said steam, secondary steam andwater separating means external of said drum arranged to receive thesteam discharged from said drum, a superheater inlet header arranged toreceive the steam from said secondary separator, means within saidheader for condensing a minor portion of said steam and separating thecondensed moisture from the remainder of said steam, and means forremoving said separated moisture from the superheater inlet header outof the flow path of said steam.

6. In a steam generating and superheating unit, a steam and water drum,means for supplying a steam and water mixture to said drum, means withinsaid drum for separating entrained water from said steam, a secondarysteam and water separator external of and arranged to receive the steamdischarged from said drum, said secondary separator including a closedcylindrical vessel having a tangential steam inlet duct and centrallylocated top and bottom outlets for steam and water respectively, asuperheater inlet header arranged to receive the steam from saidsecondary separator means within said header for condensing a minorportion of said steam and separating moisture from the remainder of saidsteam, and means for removing said separated moisture from thesuperheater inlet header out of the flow path of said steam.

7. The method of purifying substantially dry saturated steam having apressure in excess of 450 p. s. i. a. which comprises the steps ofadiabatically expanding said steam to condense moisture therein, andseparating the condensed moisture from the flow path of said expandedsteam.

8. The method of determining the purity of substantially dry saturatedsteam having a pressure in excess of 4-50 p. s. i. a. which comprisesthe steps of adiabatically expanding a sample of said steam to condensemoisture therein, separating the condensed moisture from said expandedsteam, and separately testing the condensed moisture and the expandedsteam for electric conductivity to determine the impurities in saidsteam sample.

References Cited in the tile of this patent UNITED STATES PATENTS727,480 Stevens May 5, 1903 984,047 Touzlin Feb. 14, 1911 1,327,835McKibben Jan. 13, 1920 1,795,890 Riegel Mar. 10, 1931 1,798,032 RiceMar. 24, 1931 1,901,912 Kerr Mar. 21, 1933 2,007,966 Fletcher July 16,1935 2,119,288 Raymond May 31, 1938 2,235,892 Kuhner Mar. 25, 19412,243,436 Mumford May 27, 1941 2,289,969 Kerr July 14, 1942 2,289,970Rowland et a1 July 14, 1942 2,303,572 Mumford et a1. Dec. 1, 19422,326,491 Place Aug. 10, 1943 2,353,776 Wegmann July 18, 1944 2,472,101Frisch June 7, 1949 2,532,332 Rowand Dec. 5, 1950 FOREIGN PATENTS173,557 Great Britain Dec. 20, 1921

